A known mode of an inexpensive and compact millimeter-wave communication module is a millimeter-wave communication module including a post-wall waveguide (hereinafter referred to also as “PWW”) (see, for example, Patent Literature 1).
A PPW includes a printed circuit board having a front surface and a back surface each provided with an earth conductor, the printed circuit board containing a plurality of conductor columns serving as post walls and arranged in such a manner as to stand between the earth conductor layers. The conductor columns correspond to metal sidewalls of a conventional waveguide. A millimeter-wave communication module including a PPW is configured such that (i) a wireless telecommunication IC mounted on the substrate of the PWW is, for example, wire-bonded or bump-connected to a transmission line (for example, a microstrip line, a coplanar line, or a strip line) and that (ii) a conductor pin connected to the transmission line and serving as a power feeding section is inserted in the PPW. This configuration causes a millimeter wave signal outputted by the wireless telecommunication IC to propagate through the transmission line via the pin to be finally guided to the PPW.
The conductor pin inserted in the PPW is made of (i) a metal film disposed on the entire inner wall of a non-through hole in the substrate or (ii) metal filling such a non-through hole. There have been known methods for, in the case where the conductor pin is made of a metal film, forming a metal film simultaneously with the formation of an earth electrode for the PPW. An example method is a method including (i) forming a non-through hole in a substrate, (ii) forming a metal film by sputtering from the side of the opening of the non-through hole on a surface of the substrate and on the inner wall of the non-through hole, and (iii) performing a plating process to simultaneously form a metal film for an earth electrode and a metal film for a conductor pin.